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Determining the Frequency of a String’s Appearance - PHP

In this fourth part of a five-part series on strings and regular expressions in PHP, you'll learn how to perform complex string parsing, find the last occurrence of a string, and more. This article is excerpted from chapter nine of the book Beginning PHP and Oracle: From Novice to Professional, written by W. Jason Gilmore and Bob Bryla (Apress; ISBN: 1590597702).

  1. Parsing Strings and Regular Expressions
  2. Finding the Last Occurrence of a String
  3. Retrieving Part of a String
  4. Determining the Frequency of a String’s Appearance
By: Apress Publishing
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July 08, 2010

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Thesubstr_count()function returns the number of times one string occurs within another. Its prototype follows:

int substr_count(string str, string substring)

The following example determines the number of times an IT consultant uses various buzzwords in his presentation:

    $buzzwords = array("mindshare", "synergy", "space");

    $talk = <<< talk
    I'm certain that we could dominate mindshare in this space with
    our new product, establishing a true synergy between the marketing
    and product development teams. We'll own this space in three months.

    foreach($buzzwords as $bw) {
        echo "The word $bw appears ".substr_count($talk,$bw)." time(s).<br />";

This returns the following:

The word mindshare appears 1 time(s).
The word synergy appears 1 time(s).
The word space appears 2 time(s).

Replacing a Portion of a String with Another String

Thesubstr_replace()function replaces a portion of a string with a replacement string, beginning the substitution at a specified starting position and ending at a predefined replacement length. Its prototype follows:

string substr_replace(string str, string replacement, int start [, int length])

Alternatively, the substitution will stop on the complete placement ofreplacementinstr. There are several behaviors you should keep in mind regarding the values ofstartandlength:

  1. Ifstartis positive,replacementwill begin at characterstart
  2. Ifstartis negative,replacementwill begin atstrlength -start
  3. Iflengthis provided and is positive,replacementwill belengthcharacters long. 
  4. Iflengthis provided and is negative,replacementwill end atstrlength -lengthcharacters.

Suppose you built an e-commerce site and within the user profile interface you want to show just the last four digits of the provided credit card number. This function is ideal for such a task:

$ccnumber = "1234567899991111";
echo substr_replace($ccnumber,"************",0,12);

This returns the following:


Please check back next week for the conclusion to this article.

>>> More PHP Articles          >>> More By Apress Publishing

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